The present invention relates generally to an automatic transmission with a plurality of frictional engagement elements, and an apparatus and method for controlling such an automatic transmission, and more particularly to canceling an inertia torque caused due to change in a rotational state during a gear shift.
In general, a gear shift of an automatic transmission requires shifting a frictional engagement element such as a clutch from a disengaged state to an engaged state or from an engaged state to disengaged state. It is desired to carry out such a gear shift smoothly and quickly so as to cause no gear shift shock, by suitably operating the frictional engagement element. In the case of an upshift of an automatic transmission, it is desired to absorb an inertia torque caused due to change in a rotational state of the automatic transmission.
Japanese Patent Application Publication No. 10-184410 shows a technique for an upshift of an automatic transmission. According to this technique, an upshift is implemented by engaging a to-be-engaged clutch by supplying a fluid pressure PA, and by disengaging a to-be-disengaged clutch by stopping to supply a fluid pressure PB. This clutch changeover is implemented by increasing the fluid pressure PA toward a target value PTA, and then by increasing the fluid pressure PA at a rate of change ΔPTA until a change in an input speed is actually detected (ΔN≧dNs) after the fluid pressure PA reaches the target value PTA The target value PTA, which is corresponding to a state just before the input speed starts to change, is calculated on the basis of an input torque. The rate of change ΔPTA is calculated on the basis of a target rate of change of the input speed. When the fluid pressure PA reaches the target value PTA, an engine torque TC starts to be reduced. The reduction of engine torque TC serves to absorb an inertia torque caused due to change in the input speed.